ACPAtmospheric Chemistry and PhysicsACPAtmos. Chem. Phys.1680-7324Copernicus PublicationsGöttingen, Germany10.5194/acp-8-6995-2008Monthly-averaged anthropogenic aerosol direct radiative forcing over the Mediterranean based on AERONET aerosol propertiesBergamoA.1TafuroA. M.1KinneS.2De TomasiF.1PerroneM. R.11CNISM, Physics Department, University of Salento, Italy2Max Planck Institute für Meteorologie, Hamburg, Germany0412200882369957014This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from http://www.atmos-chem-phys.net/8/6995/2008/acp-8-6995-2008.htmlThe full text article is available as a PDF file from http://www.atmos-chem-phys.net/8/6995/2008/acp-8-6995-2008.pdf

The all-sky direct radiative effect by anthropogenic aerosol (DRE<sub>a</sub>) is
calculated in the solar (0.3–4 μm) and infrared (4–200 μm)
spectral ranges for six Mediterranean sites. The sites are differently
affected by pollution and together reflect typical aerosol impacts that are
expected over land and coastal sites of the central Mediterranean basin.
Central to the simulations are aerosol optical properties from AERONET
sun-/sky-photometer statistics for the year 2003. A discussion on the
variability of the overall (natural + anthropogenic) aerosol properties with
site location is provided. Supplementary data include MODIS satellite sensor
based solar surface albedos, ISCCP products for high- mid- and low cloud
cover and estimates for the anthropogenic aerosol fraction from global
aerosol models. Since anthropogenic aerosol particles are considered to be
smaller than 1 μm in size, mainly the solar radiation transfer is
affected with impacts only during sun-light hours. At all sites the (daily
average) solar DRE<sub>a</sub> is negative all year round at the top of the
atmosphere (ToA). Hence, anthropogenic particles produce over coastal and
land sites of the central Mediterranean a significant cooling effect.
Monthly DRE<sub>a</sub> values vary from site to site and are seasonally dependent
as a consequence of the seasonal dependence of available sun-light and
microphysical aerosol properties. At the ToA the monthly average DRE<sub>a</sub>
is &minus;(4&plusmn;1) W m<sup>&minus;2</sup> during spring-summer (SS, April–September) and
&minus;(2&plusmn;1) W m<sup>&minus;2</sup> during autumn-winter (AW, October–March) at the
polluted sites. In contrast, it varies between &minus;(3&plusmn;1) W m<sup>&minus;2</sup> and
&minus;(1&plusmn;1) W m<sup>&minus;2</sup> on SS and AW, respectively at the less polluted site.
Due to atmospheric absorption the DRE<sub>a</sub> at the surface is larger than at
the ToA. At the surface the monthly average DRE<sub>a</sub> varies between the
most and the least polluted site between &minus;(7&plusmn;1) W m<sup>&minus;2</sup> and
&minus;(4&plusmn;1) W m<sup>&minus;2</sup> during SS, and between &minus;(4&plusmn;3) W m<sup>&minus;2</sup> and &minus;(1&plusmn;1) W m<sup>&minus;2</sup>
during AW. The DRE<sub>a</sub> at infrared wavelengths is positive but
negligible, especially at the ToA (&lt;0.3 W m<sup>&minus;2</sup>). The average of
DRE<sub>a</sub> monthly-means referring to all sites has allowed getting a ToA-
and sfc-DRE<sub>a</sub> yearly-mean value of &minus;(3&plusmn;2) and &minus;(5&plusmn;3) W m<sup>&minus;2</sup>,
respectively at solar wavelengths. Last data, even if refer to a
particular year, indicate that the radiative energy-balance of Central
Mediterranean land and coastal sites is quite affected by anthropogenic
particles.